Re: [PATCH v2] mm/memory-failure: fix deadlock when hugetlb_optimize_vmemmap is enabled

[Sidhartha Kumar <sidhartha.kumar@oracle.com>]

On 4/11/24 7:57 PM, Miaohe Lin wrote:
> When I did hard offline test with hugetlb pages, below deadlock occurs:
> 
> ======================================================
> WARNING: possible circular locking dependency detected
> 6.8.0-11409-gf6cef5f8c37f #1 Not tainted
> ------------------------------------------------------
> bash/46904 is trying to acquire lock:
> ffffffffabe68910 (cpu_hotplug_lock){++++}-{0:0}, at: static_key_slow_dec+0x16/0x60
> 
> but task is already holding lock:
> ffffffffabf92ea8 (pcp_batch_high_lock){+.+.}-{3:3}, at: zone_pcp_disable+0x16/0x40
> 
> which lock already depends on the new lock.
> 
> the existing dependency chain (in reverse order) is:
> 
> -> #1 (pcp_batch_high_lock){+.+.}-{3:3}:
>         __mutex_lock+0x6c/0x770
>         page_alloc_cpu_online+0x3c/0x70
>         cpuhp_invoke_callback+0x397/0x5f0
>         __cpuhp_invoke_callback_range+0x71/0xe0
>         _cpu_up+0xeb/0x210
>         cpu_up+0x91/0xe0
>         cpuhp_bringup_mask+0x49/0xb0
>         bringup_nonboot_cpus+0xb7/0xe0
>         smp_init+0x25/0xa0
>         kernel_init_freeable+0x15f/0x3e0
>         kernel_init+0x15/0x1b0
>         ret_from_fork+0x2f/0x50
>         ret_from_fork_asm+0x1a/0x30
> 
> -> #0 (cpu_hotplug_lock){++++}-{0:0}:
>         __lock_acquire+0x1298/0x1cd0
>         lock_acquire+0xc0/0x2b0
>         cpus_read_lock+0x2a/0xc0
>         static_key_slow_dec+0x16/0x60
>         __hugetlb_vmemmap_restore_folio+0x1b9/0x200
>         dissolve_free_huge_page+0x211/0x260
>         __page_handle_poison+0x45/0xc0
>         memory_failure+0x65e/0xc70
>         hard_offline_page_store+0x55/0xa0
>         kernfs_fop_write_iter+0x12c/0x1d0
>         vfs_write+0x387/0x550
>         ksys_write+0x64/0xe0
>         do_syscall_64+0xca/0x1e0
>         entry_SYSCALL_64_after_hwframe+0x6d/0x75
> 
> other info that might help us debug this:
> 
>   Possible unsafe locking scenario:
> 
>         CPU0                    CPU1
>         ----                    ----
>    lock(pcp_batch_high_lock);
>                                 lock(cpu_hotplug_lock);
>                                 lock(pcp_batch_high_lock);
>    rlock(cpu_hotplug_lock);
> 
>   *** DEADLOCK ***
> 
> 5 locks held by bash/46904:
>   #0: ffff98f6c3bb23f0 (sb_writers#5){.+.+}-{0:0}, at: ksys_write+0x64/0xe0
>   #1: ffff98f6c328e488 (&of->mutex){+.+.}-{3:3}, at: kernfs_fop_write_iter+0xf8/0x1d0
>   #2: ffff98ef83b31890 (kn->active#113){.+.+}-{0:0}, at: kernfs_fop_write_iter+0x100/0x1d0
>   #3: ffffffffabf9db48 (mf_mutex){+.+.}-{3:3}, at: memory_failure+0x44/0xc70
>   #4: ffffffffabf92ea8 (pcp_batch_high_lock){+.+.}-{3:3}, at: zone_pcp_disable+0x16/0x40
> 
> stack backtrace:
> CPU: 10 PID: 46904 Comm: bash Kdump: loaded Not tainted 6.8.0-11409-gf6cef5f8c37f #1
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.14.0-0-g155821a1990b-prebuilt.qemu.org 04/01/2014
> Call Trace:
>   <TASK>
>   dump_stack_lvl+0x68/0xa0
>   check_noncircular+0x129/0x140
>   __lock_acquire+0x1298/0x1cd0
>   lock_acquire+0xc0/0x2b0
>   cpus_read_lock+0x2a/0xc0
>   static_key_slow_dec+0x16/0x60
>   __hugetlb_vmemmap_restore_folio+0x1b9/0x200
>   dissolve_free_huge_page+0x211/0x260
>   __page_handle_poison+0x45/0xc0
>   memory_failure+0x65e/0xc70
>   hard_offline_page_store+0x55/0xa0
>   kernfs_fop_write_iter+0x12c/0x1d0
>   vfs_write+0x387/0x550
>   ksys_write+0x64/0xe0
>   do_syscall_64+0xca/0x1e0
>   entry_SYSCALL_64_after_hwframe+0x6d/0x75
> RIP: 0033:0x7fc862314887
> Code: 10 00 f7 d8 64 89 02 48 c7 c0 ff ff ff ff eb b7 0f 1f 00 f3 0f 1e fa 64 8b 04 25 18 00 00 00 85 c0 75 10 b8 01 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 51 c3 48 83 ec 28 48 89 54 24 18 48 89 74 24
> RSP: 002b:00007fff19311268 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
> RAX: ffffffffffffffda RBX: 000000000000000c RCX: 00007fc862314887
> RDX: 000000000000000c RSI: 000056405645fe10 RDI: 0000000000000001
> RBP: 000056405645fe10 R08: 00007fc8623d1460 R09: 000000007fffffff
> R10: 0000000000000000 R11: 0000000000000246 R12: 000000000000000c
> R13: 00007fc86241b780 R14: 00007fc862417600 R15: 00007fc862416a00
> 
> In short, below scene breaks the lock dependency chain:
> 
>   memory_failure
>    __page_handle_poison
>     zone_pcp_disable -- lock(pcp_batch_high_lock)
>     dissolve_free_huge_page
>      __hugetlb_vmemmap_restore_folio
>       static_key_slow_dec
>        cpus_read_lock -- rlock(cpu_hotplug_lock)
> 
> Fix this by calling drain_all_pages() instead.
> 
> Fixes: a6b40850c442 ("mm: hugetlb: replace hugetlb_free_vmemmap_enabled with a static_key")
> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
> Acked-by: Oscar Salvador <osalvador@suse.de>
> Cc: <stable@vger.kernel.org>
> ---
> v2:
>   collect Acked-by tag and extend comment per Oscar. Thanks.
> ---
>   mm/memory-failure.c | 16 +++++++++++++---
>   1 file changed, 13 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index edd6e114462f..c6750509d74c 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -153,11 +153,21 @@ static int __page_handle_poison(struct page *page)
>   {
>   	int ret;
>   
> -	zone_pcp_disable(page_zone(page));
> +	/*
> +	 * zone_pcp_disable() can't be used here. It will hold pcp_batch_high_lock and
> +	 * dissolve_free_huge_page() might hold cpu_hotplug_lock via static_key_slow_dec()
> +	 * when hugetlb vmemmap optimization is enabled. This will break current lock
> +	 * dependency chain and leads to deadlock.
> +	 * Disabling pcp before dissolving the page was a deterministic approach because
> +	 * we made sure that those pages cannot end up in any PCP list. Draining PCP lists
> +	 * expels those pages to the buddy system, but nothing guarantees that those pages
> +	 * do not get back to a PCP queue if we need to refill those.
> +	 */
>   	ret = dissolve_free_huge_page(page);

Hi Miaohe,

I recently sent a patch[1] to convert dissolve_free_huge_page() to folios which 
changes the function name and the name referenced in the comment so this will 
conflict with my patch. It's in mm-unstable now, would you be able to rebase to 
that in a new version?

Thanks,
Sid

[1] 
https://lore.kernel.org/linux-mm/20240411164756.261178-1-sidhartha.kumar@oracle.com/T/#u


> -	if (!ret)
> +	if (!ret) {
> +		drain_all_pages(page_zone(page));
>   		ret = take_page_off_buddy(page);
> -	zone_pcp_enable(page_zone(page));
> +	}
>   
>   	return ret;
>   }